Now, her darling baby boy had returned, all grown up.
       And she might have to kill him.

[cut]

The problem is the tense agreement, "had returned" versus "might have to
kill".  Any opinions would be appreciated, even if you just think the
original version is fine.

------RM

The problem is actually in the first sentence. "Now" requires the present 
perfect, not the past perfect. 

  He has returned now.
  He had returned now.

The two clauses don't have to agree, but if you change this then the two 
sentences are closer in tense.

  Now, her darling baby boy has returned, all grown up.
  And she might have to kill him.